Phosphorus Nutrition of Alfalfa

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Phosphorus Nutritionof Alfalfa
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Phosphorus (P) Nutritionof Alfalfa
Outline

• U.S. alfalfa hay yields keep increasing
• Nutrient uptake and removal
• Alfalfa root development
• General P nutrition
• P boosts hay yield, recovery, and quality
• P inputs frequency and source
• Requirement for balanced nutrition

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U.S. Alfalfa Hay YieldsAn Upward Trend
Year
Source USDA-NASS
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Record YieldResearchers at University of
Arizona(Yuma) set record for alfalfa yieldin a
year24.1 tons/A alfalfa hay in10 cuttings

• Optimal and uniform irrigation
• Chopped hay removed immediately after cutting
• N fertilizer regularly added was it needed?
• 460 lb P2O5/A added before planting
• K management unknown
• 1,440 lb K2O and 360 lb P2O5/A removed in hay

Ludwick, 2000 Arizona
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Alfalfa Nutrient Uptakeand Removal

• Alfalfa has higher demandfor nutrients than most
  crops

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Alfalfa Root Development

• Most lateral roots are near the soil surface for
  the first year, but more deep lateral roots
  develop as the plant ages
• Alfalfa has lower root density than many
  grasses and a deeper rooting zone
• P and K application increase root growth,
  enabling roots to obtain moisture and nutrients
  from greater volume of soil

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Phosphorus in Soils

• Total P in many soils (0 to 6 in.) ranges from
  400 to 2,000 lb/Abut only a fraction of that is
  available for plant uptake each season

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The primary cause of low, short-term uptakeof P
fertilizer

• The inability of P to move to absorbing roots

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Temperature Effect on Nutrient Uptake

• Cool soil temperatures will
• slow nutrient release from soil organic matter
• reduce diffusion of nutrients to the roots
• hinder root absorption and translocation

Adequate P is essential for strong root
systems Higher levels of nutrients are needed to
support vigorous plant growth in cool soil
conditions
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P Functions in Plants

• Energy storage and transfer
• Phosphate compounds are energy currency
• (such as ADP and ATP)
• Structural component of biochemicals
• Seed formation
• Calcium and magnesium phytate
• Maintenance and transfer of genetic code
• Root growth, rapid crop establishment
• Early maturity, quicker recovery

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P Fertilization Increases Nodulation
Azcon et al., 1988
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P Fertilization Increases Nodule Growth
Gates, 1974
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P Improves Alfalfa Growth and Recovery
Alfalfa regrows faster after cutting with
adequate P
Alfalfa develops more shoots after cutting with
adequate P
Li et al., 1998
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P Response Timing and Application Study

• Six-year study initiated to evaluate effect of P
  timing and application method
• Broadcast or banded P fertilizer
• Frequency
• 100 lb P2O5/A every year
• 200 lb P2O5/A every 2 years
• 600 lb P2O5/A in a one-time preplant application
• Total 6-year P rate was the same for all
  treatments variables were timing and placement

Mullen et al., 2000 OK
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Yield Response to P inYears One and Six
Mullen et al., 2000 OK
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Yield ResponseMethod and Timing
Mullen et al., 2000 OK
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Increase in Alfalfa GrowthDue to P
Fertilization(split over 5 years or one-time
application)
Mullen et al., 2000 OK
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Increase in Alfalfa GrowthDue to P
Fertilization(split over 5 years or one-time
application)
Mullen et al., 2000 Alberta
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Influence of P Application on Increasing Alfalfa
Yield (one-time application or annual
application)
Mullen et al., 2000 Alberta
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Influence of P Application on Increasing Alfalfa
Yield (one-time application or annual
application)
Mullen et al., 2000 Alberta
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Alfalfa Response toAdded P Fertilizer

• Yield response to added P most evident at first
  cutting
• Soil P fertility was maintained by small annual
  applications or a large one-time application

James, 1995 Utah
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Established StandsOften Need Additional P

• Soil testing and tissueanalysis can revealneed
  for fertilization.
• P fertilizer does not movefar in soil
• Soil incorporationprior to planting is best
• Top-dressed and irrigated P is suitablefor
  subsequent fertilization
• P moves during freeze/thaw cycles, washes into
  soil cracks, and is taken up by shallow surface
  roots and crowns ? and becomes available for
  plant uptake.

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What P Source Is Superiorfor Alfalfa?

• Three-year study with 24 cuttings
• 10-34-0 applied in irrigation water
• 10-34-0 sprayed on soil surface
• 11-52-0 granules broadcast applied
• (0, 20,40, 60, 100 lb P2O5/A/yr for 3 years)
• Positive hay yield response to P, but
• No differences in P sources or methodsof
  application in yield or tissueP concentration

Ottman et al., 2001 AZ
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P Source? Not a Significant Factor for Alfalfa
Yields

• Four P sources compared(2 liquid, 2 solid)
• Yield response to P fertilization(11 to 27
  increase) under irrigation
• No differences in P fertilizersources
• Placement compared
• Surface banding or broadcast onestablished
  alfalfa stands
• No yield differences due tofertilizer placement

Koenig, 2003 Utah
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Effect of P Fertilizeron Soil P Concentrations

• Failure to replace harvested nutrients will
  gradually deplete soil nutrient supply and reduce
  yields

Cihacek, 1993 NM
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Preparing the Soil Before Planting Is Key

• Prior to planting
• Incorporate P forestablishment of strongroot
  systems, promotingrapid recovery,
  andmaintaining healthy stands
• Provide balanced nutritionAdequate K, Ca, Mg,
  S, B, etc.
• Eliminate soil pH problems - alfalfa does not
  thrive in acid soils

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Balanced P and K NutritionIs Essential for
OptimalYields and Stand Maintenance
Berg et al., 2005 IN
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Proper Attention to All Nutrients Is Required
for Healthy Plants and High Yield Levels
Berg et al., 2005 IN
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General Guidelines for P Fertilization

• Use soil testing to guide P fertilization
  decisions and use local recommendations for best
  results
• Incorporate adequate P into the top 2 to 6 in. of
  soil prior to planting to meet the first years of
  productionand nutrient removal in harvested hay
• Use tissue analysis to determine need for
  subsequent-year phosphate
• Application can be made any time of the year--
  frequently during winter months to meet the
  high-demand period in the Spring
• (avoiding application to snow-covered, frozen, or
  saturated fields with the potential risk of
  runoff)

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Diagnosis of P Deficiencies

• Visual Observation
• Distinct P deficiencies are seldom observableon
  alfalfa not an effective diagnostic method!
• Soil Testing
• Soil test prior to planting and regularly
  afterwards
• Tissue Analysis
• Best way to monitor plant performance andprevent
  hidden hunger and yield loss
• Recommended tissue concentration
• 0.25 to 0.40 P in top third of plant

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Both P Fertilizer and Animal Manure Provide
Nutrition for Alfalfa
Cumulative alfalfa yield, g/pot
Goss Stewart, 1979 Texas
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Manure Management

• Manure supplies many nutrients but not in the
  ratio required for crops
• Physical problems compaction, crown
  damage,leaf burn, salinity
• Nutritional problems N can stimulate weeds,
  extra Kcan cause cation imbalance for dairy feed
  rations
• Excessive manure applicationmay buildup P
  concentrations to levelsof concern in water
  runoff

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Summary-P Nutrition of Alfalfa

• Alfalfa roots grow best in nutrient-rich soil
  Prepare the seedbed prior to planting and
  supplement in later years as needed
• Adequate P promotes vigorous N2 fixation, shoot
  development, and faster regrowth after cutting
• Uptake of P continues through the season and is
  harvested in large amounts. The P fertilizer
  source is not important
• Placement near the seedling boosts establishment
  and stand longevity
• Crop response to P is best predicted with a soil
  test and subsequent tissue testing
• Nutrient management is an essential key to
  profitability and efficient use of other inputs

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International Plant Nutrition Institute
(IPNI)655 Engineering Drive, Suite 110Norcross,
GA 30092-2837Phone [phone] Fax
770-448-0439Website www.ipni.net
Reference 06128